System for locking interior door latches

ABSTRACT

A method, system and apparatus for centralized thermal recovery based on an oil reservoir are disclosed. The steps of the method including treating the oil reservoir with edge and bottom water layers as a whole unit; providing horizontal wells extending into the upper part of the edge and bottom water layers with an electric heating system configured to be positioned in each horizontal well; continuously centralized electric heating the edge and bottom water until temperature of the whole oil reservoir rises to the flowing state of formation oil; and then centralized thermal recovery is carried out by several recovery mechanisms in addition to viscosity reduction and gravity-assisted oil recovery. An electric heating system is also disclosed including an inner liner, ferrite permanent magnet rods, waterproof spiral electric heaters, an insulation board and a sealing board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part application of pending U.S. Patent Publication No. 2017-0002637 A1 published May 28, 2015 and Ser. No. 15/039,454, which claims priority to China Application No. 201310689685.0 filed Dec. 12, 2013, all of which are hereby incorporated herein in their entireties by reference.

FIELD OF THE INVENTION

Present invention is applicable to oil and gas reservoirs with edge and bottom water, such as heavy oil reservoirs and high pour-point oil reservoirs, which can be thermally recovered in oil industry. It is mainly proposed to solve the problems of high viscosity or wax content of crude oil, low thermal recovery efficiency of steam stimulation or steam flooding, short stable production time, high decline rate and low recovery degree.

BACKGROUND OF THE INVENTION

Huff and puff or steam stimulation, steam flooding, hot-water flooding and in-situ combustion are all efficient technical methods in thermal recovery. However, with gradually in-depth development, more and more problems have been exposed in production. Especially for middle-deep to super-deep reservoirs (depth of 600˜2300 m), the contradiction in production is more prominent: 1) As pipeline and wellbore heat loss in steam huff and puff, steam drive, hot water drive is serious, thermal efficiency is low, water production rate of production wells is high, production rate is low, decline rate is high, the ultimate recovery degree of reservoir is affected; 2) although in-situ combustion is effective to production test of some common-heavy oil fault blocks and can satisfy the requirement of industry production, it cannot be applied to most of the super-heavy oil reservoirs, in addition, the method is destructive to the reservoir. Once the reservoir is destroyed, any advanced thermal recovery method invented in the future will be impossible for operation; 3) at present, electric heating method is confined to the sucker rod and wellbore heating method. Its purpose is to improve the oil and gas lifting ability capacity of the production wells, and to reduce oil viscosity and wax deposition of crude oil around the production wells; 4) horizontal well hydraulic fracturing and electric heating oil shale in-situ thermal recovery method is difficult to implement in heavy oil reservoirs, high cost and serious environmental pollution; 5) at present, all thermal recovery methods belong to a method of local heating oil layers. Oil layers are heated unevenly, the thermal holding time is short, the efficiency is low, and the remaining oil has high oil saturation, which is mainly concentrated in the areas with low thermal energy and low thermal efficiency.

SUMMARY OF THE INVENTION

Trap is a place where oil and gas can continue to migrate and gather in it. The trap consists of three parts: reservoir, cap rock and barrier which prevents oil and gas from migrating and causes oil and gas accumulation. It can be the bending deformation of cap rock itself, such as anticline, or other barrier, such as fault, lithological change, etc. In a word, traps are effective space for capturing dispersed hydrocarbons to form hydrocarbon accumulation, and have the ability to store oil and gas, but there are not always oil and gas in traps. Once a sufficient amount of oil and gas enters the trap, fills the trap or occupies a part of the trap, oil and gas reservoirs can be formed. Any oil and gas reservoir with edge and bottom water can be treated as a whole unit sealed by cap rock and barriers including anticline structure, fault, lithological change, edge and bottom water, etc.

In accordance with the invention, there is provided a method of centralized thermal recovery based on an oil reservoir comprising the steps of: treating the whole oil reservoir with edge and bottom water as a integrated unit sealed by cap rock, barrier including edge and bottom water, etc.; providing at least one or more horizontal wells extending into edge and bottom water layers at a depth below the oil-water interface, near the oil layers, with an electric heating system configured to be positioned in each horizontal well; continuously centralized electric heating the edge and bottom water with electric heating system and thermal energy gradually accumulates in the oil reservoir until temperature of the whole oil reservoir rises to the state of the crude oil in place becoming mobile and flowing; centralized excavating the crude oil with at least one or more production wells; after the completion of primary oil recovery, the residual oil and water in reservoir can be separated by gravity and the formation water can be re-heated for secondary oil recovery.

In another embodiments, a concentrated thermal recovery method based on an oil reservoir comprising treating the whole oil reservoir with edge and bottom water as a integrated unit sealed by cap rock, barrier including edge and bottom water, etc. comprising the direction of heat transfer is mainly upward and the heat conduction velocity of reservoir is higher than that of surrounding rocks and the thermal insulation effect of surrounding rock is high therefore the heat can be continuously transferred upward and accumulated gradually in the oil reservoir.

In another embodiments, a concentrated thermal recovery method based on an oil reservoir comprising treating the whole oil reservoir with edge and bottom water as a integrated unit sealed by cap rock, barrier including edge and bottom water, etc. comprising most of the reservoirs develop edge and bottom water and contain adequate formation water resources which make it possible that horizontal wells continuously electric heat edge and bottom water for a long time and supply substantial thermal energy to the oil reservoir.

In further embodiments, a concentrated thermal recovery method based on an oil reservoir comprising providing at least one or more horizontal wells extending into edge and bottom water layers at a depth below the oil-water interface, near the oil layers comprising horizontal wells can be sidetracking horizontal wells of original production wells, or they can be horizontal wells that meet water layers alone.

In further embodiments, a concentrated thermal recovery method based on an oil reservoir comprising providing at least one or more horizontal wells extending into edge and bottom water layers at a depth below the oil-water interface, near the oil layers comprising horizontal wells can be independent horizontal wells or multi-branch horizontal wells.

In further embodiments, a concentrated thermal recovery method based on an oil reservoir comprising providing at least one or more horizontal wells extending into edge and bottom water layers at a depth below the oil-water interface, near the oil layers comprising horizontal wells are equably arranged on a horizontal plane in the edge and bottom water layer.

In further embodiments, a concentrated thermal recovery method based on an oil reservoir comprising providing at least one or more horizontal wells extending into edge and bottom water layers at a depth below the oil-water interface, near the oil layers comprising the depth determination depends on reservoir volume. The larger the volume, the deeper the depth.

In another embodiments, a concentrated thermal recovery method based on an oil reservoir comprising an electric heating system comprising: an inner liner positioned in the horizontal well comprising the upper half of the inner liner slotted and the lower half of the inner liner vacuum-sealed; a heat insulation board set at a horizontal diameter of the inner liner, several ferrite permanent magnet rods fixed on the inner wall of the upper half inner liner; a waterproof spiral electric immersion heater connected in series provided on the heat insulation board in the middle of the upper liner; wherein the lower liner is vacuum-sealed by a sealing board in cooperation with the heat insulation board.

In another embodiments, a concentrated thermal recovery method based on an oil reservoir comprising an electric heating system comprising

-   -   the upper half of the inner liner slotted to allow formation         water flowing freely;     -   and the lower half of the inner liner vacuum-sealed to prevent         thermal energy from transferring downwards;     -   the whole inner liner provided to support the ferrite permanent         magnet rods, the waterproof spiral electric immersion heater and         the heat insulation board;     -   a heat insulation board set at a horizontal diameter of the         inner liner to prevent thermal energy from transferring         downwards;     -   several ferrite permanent magnet rods fixed on the inner wall of         the upper half inner liner to prevent scale;     -   a waterproof spiral electric immersion heater connected in         series provided on the heat insulation board in the middle of         the upper liner to generate resistant heat;     -   a sealing board set at two sides of the lower half of the inner         liner in cooperation with the heat insulation board to prevent         thermal energy from transferring downwards, and     -   to keep the stability of the lower half of the inner liner.

In accordance with the invention, a method of centralized thermal recovery based on an oil reservoir comprising continuously centralized electric heating the edge and bottom water with electric heating system until the temperature of the whole oil reservoir increases to the state that all of in-place oil becomes mobile and flows comprising edge and bottom water playing prominent roles during the process of concentrated electric heating and concentrated oil production:

-   -   the edge and bottom water is treated as heat transfer medium;     -   the edge and bottom water is treated as a coolant of the         immersion heaters;     -   the edge and bottom water is treated as a sort of protection for         petrophysical characteristics of porosity and permeability for         its relatively stable salinity similar to that of pore water in         the oil reservoir,     -   the edge and bottom water protects crude oil from heat damage         because of its relative lower boiling temperature under certain         pressure;     -   the edge and bottom water has capacity of heat storage, and can         keep preheated reservoir warm throughout the whole process of         centralized thermal recovery;     -   the edge and bottom water is treated as one of sources of steam         flooding energy in the process of centralized oil production;     -   the edge and bottom water coning is treated as a resource of hot         edge and bottom water driving energy in the process of         centralized oil production;     -   because of the strong fluidity and high thermal conductivity of         water, it can decrease the well pattern density of electric         heating horizontal wells;     -   the edge and bottom water flowing up and down is treated as a         source of induced heat provided the electric immersion heater         passes current which induces induced current in water due to its         electrical conductivity;     -   Influenced by geothermal gradient, the deeper the formation         water is buried, the higher the formation water temperature is,         and the more energy-saving electric heating the edge and bottom         water is;     -   because of the direction of heat transferring mainly upward, the         gravity differentiation of hot and cold water, as well as the         fact that thermal conductivity of surrounding rock is worse than         that of reservoir, the thermal energy in edge and bottom water         mainly transfers upward with less heat loss and most accumulates         in the oil reservoir and the edge bottom water layer above the         horizontal wells plane;     -   edge and bottom water resources are abundant and environmentally         friendly, therefore the method of electric beating edge and         bottom water can be recycled.

In another embodiment, a method of centralized thermal recovery based on an oil reservoir comprising continuously centralized electric heating the edge and bottom water with electric heating system until the temperature of the whole oil reservoir increases to the state that all of in-place oil becomes mobile and flows comprising the electric heating system preferably includes a thermocouple operatively connected to the surface power unit for monitoring heating time and heating temperature, accordingly, further to control the pressure of the oil reservoir according to the congruent relationship between boiling point and pressure of water.

In further embodiment, a method of centralized thermal recovery based on an oil reservoir comprising continuously centralized electric heating the edge and bottom water with electric heating system until the temperature of the whole oil reservoir increases to the state that all of in-place oil becomes mobile and flows comprising the gradually accumulated reservoir pressure and temperature can be released with some production wells to prevent cracking in closed reservoirs.

In some embodiment, a method of centralized thermal recovery based on an oil reservoir comprising continuously centralized electric heating the edge and bottom water with electric heating system until the temperature of the whole oil reservoir increases to the state that all of in-place oil becomes mobile and flows comprising thermal energy coming from resistance heat generated by immersion electric heater and electromagnetic induction beat generated by upward moving formation water passing through electromagnetic field.

In another embodiment, a method of centralized thermal recovery based on an oil reservoir comprising providing at least one or more horizontal wells extending into at least one or more edge and bottom water layers at a depth below the oil-water interface with an electric heating system configured to be positioned in each horizontal well comprising high-power electric heating formation water to the boiling point temperature under initial formation pressure, and then lowering power continuous electric heating formation water at low-temperature.

In some embodiment, a method of centralized thermal recovery based on an oil reservoir comprising with electric heating system until the temperature of the whole oil reservoir increases to the state that all of in-place oil becomes mobile and flows comprising the temperature of the top oil reservoir rising up at least to the range of 80° C.˜150° C.

In another embodiment, a method of centralized thermal recovery based on an oil reservoir comprising continuously electric heating the edge and bottom water at a pressure lower than the reservoir fracture pressure.

In further embodiment, a method of centralized thermal recovery based on an oil reservoir comprising under a certain pressure lower than the reservoir fracture pressure comprising under certain pressure conditions, when water is heated, the water temperature will gradually rise until the boiling point temperature, and then continue to heat, the temperature will not rise along with substantial steam generated until the pressure continues to increase.

In another embodiment, a method of centralized thermal recovery based on an oil reservoir comprising continuously centralized electric heating the edge and bottom water at a temperature of the edge and bottom water around the immersion heater lower than 450° C.

In some embodiment, a method of centralized thermal recovery based on an oil reservoir comprising characteristics of temperature variation inside the oil reservoir during centralized electric heating and centralized oil production comprising during continuously electric heating the edge and bottom water layers, as heat transfers upwards, the temperature of the bottom oil reservoir is higher than that of the top oil reservoir, and the cross section temperature of electric heating horizontal well is higher than that between wells, the upper temperature of the former is equal to the middle and lower temperature of the latter. When electric heating stopped, over time, heat gradually diffuses and homogenizes in the reservoir until the end of centralized oil production.

In accordance with another embodiment, a method of centralized thermal recovery based on an oil reservoir comprising an electric heating system comprising: a connector system for connecting the electric immersion heater to an electrical cable, and, a surface power unit for delivering electrical power to the electrical heater through the electrical cable.

In further embodiments, a concentrated thermal recovery method based on an oil reservoir comprising providing at least one or more horizontal wells extending into at least one or more edge and bottom water layers at a depth below the oil-water interface with an electric heating system configured to be positioned in each horizontal well comprising a waterproof spiral electric immersion heater connected in series, when immersion heater is immersed in water, thermal energy mainly comes from resistance heat of the waterproof spiral electric heater and electromagnetic induction heat of formation water flowing up and down in the magnetic field because water itself is an electric conductor, and the water can be heated quickly. Simultaneously, the electric wire will not be burned.

The scale removal technology of magnet in electric heating can effectively solve the scale phenomenon in the process of electric heating. Scale originates from the hard water quality. Magnets can soften water, which is environmental friendly, economical, convenient and safe. Ferrite permanent magnet, whose components mainly include BaFe12019 and SrFe12019, is made by ceramic technology, bears the characteristics of well temperature resistance, moderate price, and wide application. It is a preferred material for scale removal adapted to the environment of electric heating edge and bottom water layers.

According to the size of the reservoir, horizontal wells are drilled in the upper water layer of the edge-bottom water reservoir, near the oil layer. An electric immersion heater is installed in the upper slotted inner liner of the horizontal well to conduct electric heat to the water layer.

The structure of the electric heater of horizontal well is shown in FIG. 1, detailed description is accompanied by FIG. 1a , FIG. 1b and FIG. 1c . The slotted inner liner 1 of horizontal-well 11 is divided into upper and lower parts by a heat insulation board 4. The upper part is slotted, in which several spiral electric heaters 3 connected in series are set on the board which is set at the horizontal diameter of the inner liner. In the lower part, the inner liner is sealed in vacuum by a liner sealing board 5 to insulate heat transferred downward in combination with the insulation board.

Several ferrite permanent magnet rods are fixed at the inner top of the upper slotted liner to prevent scaling.

Magnetized water scale prevention principle is cited as following:

The scale formed by water on the wall of the heater tube is hard scale CaCO₃, which is called calcite. Its physical and chemical properties are similar to those of marble, with compact arrangement and hard structure.

After magnetic treatment, the particle group of water becomes smaller, the conductance increases and the activity increases. When heated, impurities in water create a thin layer of soft dirt on the wall of the metal tube. It is characterized by loose arrangement of molecules, disorder, poor adhesion to the metal pipe wall and easy to fall off. It can be reduced and eliminated by using reliable magnetizer for a long time which has the function of differentiating and eliminating scale on existing scale device.

The magnetizer can be divided into active and passive. Active is the electromagnet, which needs power and can control the magnetization. The passive source is made of permanent magnet, which is connected to the water pipe. The water can be magnetized at any time without power supply.

Curie temperature refers to the temperature at which a material can change between a ferromagnet and a paramagnet. When it is below Curie temperature, the material becomes a ferromagnet, and the magnetic field associated with the material is difficult to change. When the temperature is higher than Curie temperature, the material becomes a paramagnet, and the magnetic field of the magnets can easily change with the change of the surrounding magnetic field. It is reported that the Curie temperature of ferrite is about 450 degrees, usually greater than or equal to 450 degrees.

In some embodiment, a method of centralized thermal recovery based on an oil reservoir comprising centralized excavating the crude oil with at least one or more production wells comprising centralized recovering the mobilized oil with at least one or more production wells which are either vertical wells or horizontal wells, or any combination of these wells.

In another embodiment, a method of centralized thermal recovery based on an oil reservoir comprising centralized recovering the mobilized oil with at least one or more production wells comprising various oil recovery mechanisms are applied to exploiting oil efficiently including

-   -   the thermal expansion pressure from water formations and oil         layers;     -   the effect of synthesis steam flooding produced by water soluble         gas overflow, steam coming from edge and bottom water as well as         pore water, and pyrolysis gas from crude oil in bottom oil         reservoirs;     -   hot water flooding due to edge and bottom hot water coning;     -   the viscosity-reduction effect/wax-precipitation effect of         in-place oil under high temperature;     -   gravity drainage of the heated crude oil;     -   gravity differentiation among fluids after primary-centralized         thermal recovery of oil for another times, and     -   combinations thereof.

BENEFICIAL EFFECT OF THE INVENTION

This is a centralized thermal recovery method based on an oil reservoir unit, i.e. unified heating and unified oil recovery for the whole reservoir, reflecting the scale effect of the whole reservoir preheating and centralized construction operation. It is different from the conventional thermal recovery method which oil is produced while heating directly oil layers in a single well or group of wells. At the same time, it is also a kind of thermal recovery method which makes full use of natural formation water resources and their attributes and heats the whole oil reservoir by electric heating of formation water in horizontal wells. It can achieve the following beneficial effects: 1) The electric heating of formation water in horizontal wells is environmentally friendly, energy-saving, convenient, fast and easy to operate; 2) Thermal energy can be transmitted to reservoirs through water layers. Adequate heat can meet the needs of thermal recovery development, to solve the problems of reservoir thermal energy injection, small heating radius and short duration of thermal energy; 3) No use of surface water resources, no steam injection and sewage treatment processes, cost reduction, energy saving and environmental protection; 4) Reservoir in-situ thermal recovery method, no pipeline and wellbore thermal loss, thermal efficiency high, can effectively develop from deep to ultra-deep thermal recovery reserves; 5) High bottom water temperature, the whole reservoir crude oil in movable temperature conditions, combined with other driving energy, bottom water coning in the process of oil recovery can effectively form bottom water hot water flooding; 6) Unlimited requirements for reservoir geological characteristics, widely used in various oil reservoirs with edge and bottom water, 7) No damage to the reservoir and multiple recovery. The centralized thermal recovery method based on an oil reservoir by horizontal wells electric heating edge and bottom water layers has natural advantages, which can effectively solve many technical problems faced by conventional thermal recovery methods at present, and improve the production degree and ultimate recovery degree of reservoir reserves; 8) This method can be widely applied in thermal recovery of other similar types of mineral resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a structure of an electric heating system positioned in a horizontal well.

FIG. 1a is a schematic diagram of the longitudinal profile of an electric heating system positioned in a horizontal well.

FIG. 1b is a schematic diagram of the cross section of an electric heating system positioned in a horizontal well.

FIG. 1c is a side view of the line of an electric heating system positioned in a horizontal well.

FIG. 2 is a schematic diagram of wellbore structure of an electric heating horizontal well for centralized thermal recovery method based on an oil reservoir by electric heating edge and bottom water layers with horizontal wells.

FIG. 3 is a schematic diagram of at least one or more electric heating horizontal wells for centralized thermal recovery method based on an oil reservoir by electric heating edge and bottom water layers with horizontal wells.

FIG. 4 is a schematic diagram of heat transfer direction of electric heating system in horizontal wells.

FIG. 5 is a schematic diagram of temperature distribution curves in oil reservoir under 15 MPa pressure during centralized thermal recovery based on an oil reservoir by numerical simulation.

DETAILED DESCRIPTION

Label 1 in each figure refers to a slotted upper inner liner. Its function mainly has two points: one is to suspend the permanent magnet rods to protect the electric heater from the pressure of the upper stratum; the other is to allow the formation water to enter and leave the slotted screen pipe freely, so that the water and the electric heater can fully contact, so as to better play the thermal conductivity of water.

Label 2 refers to ferrite permanent magnet rods used to prevent scaling. According to FIG. 5 the prediction diagram of the relationship between water boiling point temperature and pressure, the higher the formation pressure is, the higher the water boiling point temperature is, and the corresponding fitting mathematical relationship is as follows:

Y=178.27x ^(0.2509)

Note: y: Boiling point temperature; x: pressure MPa. Under the condition of electrically heated formation water, the boiling point temperature corresponding to formation water under 15 MPa is predicted to be 350 degrees Celsius and that corresponding to 28 MPa is about 450 degrees Celsius. Therefore, as long as formation pressure and the boiling point temperature of formation water are controlled to be lower than the Curie temperature 450 degrees Celsius of ferrite permanent magnet, the magnetism of permanent magnet will not be destroyed. At the same time, it must be noted that when the electric heater is DC, the magnetic pole of the ferrite permanent magnet rod must be in the same direction as the electromagnetic field produced by the electric heater. Otherwise, the magnetic force of the permanent ferrite magnet rod will gradually weaken.

Label 3 refers to waterproof spiral electric heater connected in series. The electric heater is connected to the ground power supply through a coaxial cable. When current is applied, the spiral electric heater will generate resistance heat to heat the edge and bottom water directly, the heated edge and bottom water will transfer mainly upwards and cold water will move downwards, which makes the surrounding water moving up and down produce electromagnetic induction heat. During this period, when the direction of the magnetic field is the same as that of the electromagnetic field, the ferrite permanent magnet rods will enhance the intensity of the electromagnetic field produced by the electric heater, and vice versa, weaken the induction phenomenon of the electromagnetic field.

Label 4 refers to heat insulation board. As shown in FIG. 4, the heat energy from the electric heater radiates to the surrounding area, and the upward heat is transferred with the upward movement of formation water, while the downward heat energy is reflected by the insulation plate, and only a very small amount of heat energy is transmitted downward. Another function of the heat insulation board 4 is to sustain the waterproof spiral electric heater connected in series 3.

Label 5 refers to a liner sealing board. It is well known that vacuum has good thermal insulation. The lower part of the inner liner is sealed in vacuum, which acts as a barrier to heat transfer downward together with the heat insulation board.

Label 6 in FIG. 2 refers to water and oil interface. Electric heating system is configured to be positioned in horizontal well filled with gravel for open hole completion, as label 8. Label 7 refers to reservoir top interface, and labels 6 to 7 are reservoir thickness. Label 9 refers to coaxial cable connecting power supply and electric heater. Closed waterproof treatment is needed at the joint of coaxial cable and electric heating system. Label 10 refers to power supply, provided either a DC or AC. Label 11 in FIG. 2 and FIG. 3 refers to single electric heating horizontal well extending in edge and bottom water layers.

Label 12 in FIG. 3 refers to an oil reservoir, label 13 refers to edge and bottom water layers, at least one or more single electric heating horizontal wells are provided in at least one or more edge and bottom water layers on a horizontal plane 14 below oil-water interface 6. The single horizontal wells can be substituted by branched electric heating horizontal wells in order to increase electric heating efficiency and reduce the operating cost of single horizontal wells.

FIG. 4 is a schematic diagram of heat transfer direction of electric heating system in horizontal wells. The structure design of the slotted inner liner and the upward movement of hot water ensure that thermal energy can be transferred to the reservoir through formation water medium and accumulated in the reservoir to minimize the loss of electrical and thermal energy in formation water. The most important problem here is to ensure the horizontal direction of the insulation board and the slotted screen tube above. Therefore, the sealing plate must choose a high density insulation plate, such as lead plate, or other more effective materials.

FIG. 5 is a schematic diagram of temperature distribution curves in oil reservoir under 15 MPa pressure at the time of stopping electric heating by numerical simulation. The boiling point temperature of water corresponding to the formation pressure of 15 MPa is 350 degrees Celsius, that is to say, in the oblique shaded part of the figure, wherein the temperature is up to 650 degrees Celsius which is much higher than 350 degrees Celsius, pore water in the oil reservoir exists in a vapor state. At the same time, some of the formation crude oil will be pyrolyzed, resulting in a small amount of pyrolytic gas. These factors are conducive to improving the efficiency of centralized oil recovery. When the electric heating stops and enters the production stage, the temperature inside the reservoir will drop below the boiling point temperature of water step by step, and the generation of this part of water vapor and pyrolysis gas will end.

Example

According to the size of a reservoir, horizontal wells which can be either single horizontal wells or multi-branch horizontal wells are drilled in the upper water layers, near the oil layer, which can store enough thermal energy to raise the temperature of the whole oil reservoir and delay the formation fracture due to premature boiling of the formation water and overpressure.

The number, length and trend of horizontal well are determined by the size of water body and reservoir volume. Gravel packed open hole completion works well.

If the horizontal well is sidetrack drilled from an oil production well, the conducting wire can be used as borehole or pumping rod electric heater so that the effect of cooling and heating can be realized; if the horizontal well is drilled individually, a skin heat tracing device needs to be applied to the conducting wire. High temperature resistant materials should be optimized to prevent the conducting wire from overheated in the borehole.

Pressure distribution curves in oil reservoir during centralized thermal recovery based on an oil reservoir by numerical simulation shows that the static pressure in the reservoir quickly changes to thermal expansion pressure after electric heating edge and bottom water layer, and the pressure distribution is relatively uniform, which corresponds to the boiling point temperature of formation water one by one. When the electric heating stops and enters the production stage, the reservoir enters the step-down production stage, and the pressure drop is relatively fast until the end of production, and the pressure drops to 2 MPa. Obviously, the magnitude of thermal expansion pressure plays an important role in the process of oil recovery.

Temperature distribution curves in oil reservoir during centralized thermal recovery based on an oil reservoir by numerical simulation shows that different from the characteristics of the pressure distributed in the oil reservoir, the temperature in the oil reservoir undergoes a gradual accumulation process during the centralized electric heating process. The temperature at the bottom of the reservoir is obviously higher than that at the top, and the temperature above the electric heating horizontal well is higher than that between wells. When the electric heating is stopped, the well closure is conducive to the further uniform diffusion of unbalanced heat in the oil reservoir. In the stage of centralized production, the reservoir temperature gradually decreases with the production of crude oil and becomes more uniform. Due to the thermal insulation of formation water, the reservoir temperature remained at a high level of about 180 degrees Celsius until the end of production.

After centralized electric heating the bottom water for 1100 days, the top temperature of the reservoir reaches 150 degrees Celsius. The production peak period produces 65-90 t/d of oil per day, the stable production time is 1405 days, and the recovery degree of primary production is as high as 53.8%.

Operation

Electric heaters are configured to be positioned in several horizontal wells drilled in an upper part of water layer of the reservoir, near the oil layers. The electric heaters heat the edge and bottom water layer of the reservoir so that the temperature of the whole reservoir can be increased. Several mechanisms are applied to recover oil efficiently, such as, the effect of heat transfer, the effect of steam flooding produced by water soluble gas overflow, the thermal expansion pressure from water formations and oil layers as well as the viscosity-reduction effect/wax-precipitation effect of in-place oil under high temperature.

INDUSTRIAL APPLICABILITY

It can be applied to thermally recover heavy oil reservoirs and high pour-point oil reservoirs with edge and bottom water layers, especially for those oil reservoirs in depth of middle-super deep depth which are difficulty recovered. This method can be widely applied in thermal recovery of other similar types of mineral resources. 

1. A centralized thermal recovery method based on an oil reservoir said the oil reservoir comprising at least one or more edge and bottom water layers, said the oil reservoir is at a first temperature and pressure comprising a quantity of in-place oil, said method comprising: the oil reservoir with edge and bottom water layers treated as a whole unit sealed by cap rocks and other barriers including anticline structure, fault, lithological change, edge and bottom water, providing at least one or more horizontal wells extending into at least one or more water layers at a depth below the oil-water contact, each horizontal well comprising an electric thermal recovery system comprising: an inner liner provided in a horizontal well wherein the upper half slotted and the lower half vacuum-sealed by a heat insulation plate and a sealing plate; a heat insulation plate set at a horizontal diameter of the inner liner; an electric heater configured to be positioned on the heat insulation plate in the upper part of the inner liner; a plurality of ferrite permanent magnet rods fixed at the upper inner liner; sealing plate together with heat insulation plate sealing the lower half of the inner liner; centralized electric heating at least one or more edge and bottom water layers with the electric heaters until oil reservoir temperature rises to the state of all the formation crude oil becoming mobile and flowing; and centralized recovering the mobilized oil with at least one or more production wells.
 2. The method according to claim 1 wherein: the whole oil reservoir is treated as a sealed unit to be centralized heated; the oil reservoir temperature and pressure integrally increased; all the formation crude oil in the oil reservoir is mobilized.
 3. The method according to claim 1 wherein: treating the whole oil reservoir with edge and bottom water layers as an integrated unit sealed by cap rocks, barriers including anticline structure and edge-bottom water; the reason that thermal energy can be continuously transferred upward and accumulated gradually in the oil reservoir comprising reservoirs are well connected, and heat conduction velocity of reservoir is higher than that of surrounding rocks; the direction of heat transfer is mainly upward; continuously electric heating edge and bottom water to keep thermal energy accumulated gradually in the oil reservoir. the thermal insulation effect of surrounding rock is high.
 4. The method according to claim 1 wherein the property of gravity differentiation between hot and cold water makes heat energy in edge and bottom water mainly transfer upwardly, and the cold water moving downwards can be electrically heated continuously; heat energy is mainly accumulated in upper edge and bottom water layers and oil reservoir along with a little heat energy emitting downwards.
 5. The method according to claim 1 wherein the reservoir develop edge and bottom water, and contain adequate formation water resources; horizontal wells continuously electric heat edge and bottom water for a long time and supply substantial thermal energy to the oil reservoir.
 6. The method according to claim 1 wherein horizontal wells can be sidetracking horizontal wells of original production wells, or meet water layers alone; horizontal wells can be independent or multi-branch horizontal wells; horizontal wells are equably arranged on a horizontal plane in the upper edge and bottom water layer; the depth determination of horizontal wells depends on reservoir volume, the larger the volume, the deeper the depth; the number, length and trend of horizontal wells are determined by the size of water body and reservoir volume.
 7. The method according to claim 1 wherein an electric heating system comprising: an inner liner positioned in the horizontal well comprising the upper half of the inner liner slotted to allow formation water flowing freely; and the lower half of the inner liner vacuum-sealed to prevent thermal energy from transferring downwards; the whole inner liner provided to support the ferrite permanent magnet rods, the waterproof spiral electric immersion heater and the heat insulation board; a heat insulation board set at a horizontal diameter of the inner liner to prevent thermal energy from transferring downwards; several ferrite permanent magnet rods fixed on the inner wall of the upper half inner liner to prevent scale; a waterproof spiral electric immersion heater connected in series provided on the heat insulation board in the middle of the upper liner to generate resistant heat and directly heats the edge-bottom water; a sealing board set at two sides of the lower half of the inner liner in cooperation with the heat insulation board to prevent thermal energy from transferring downwards, and keep the stability of the lower half of the inner liner.
 8. The method according to claim 1 wherein the edge and bottom water plays a prominent roles in centralized thermal recovery based on an oil reservoir comprising: the edge and bottom water is treated as heat transfer medium; the edge and bottom water is treated as a coolant of the immersion heaters; the edge and bottom water is treated as a sort of protection for petrophysical characteristics of porosity and permeability for its relatively stable salinity similar to that of pore water in the oil reservoir; the edge and bottom water protects crude oil from heat damage because of its relative lower boiling temperature under certain pressure; the edge and bottom water has capacity of heat storage, and can keep preheated reservoir warm throughout the whole process of centralized thermal recovery; the edge and bottom water is treated as one of sources of steam flooding energy in the process of centralized oil production; the edge and bottom water coning is treated as a resource of hot edge and bottom water driving energy in the process of centralized oil production: because of the strong fluidity and high thermal conductivity of water, it can decrease the well pattern density of electric heating horizontal wells; the edge and bottom water flowing up and down is treated as a source of induced heat provided the electric immersion heater passes current which induces induced current in water due to its electrical conductivity; Influenced by geothermal gradient, the deeper the formation water is buried, the higher the formation water temperature is, and the more energy-saving electric heating the edge and bottom water is; because of the direction of heat transferring mainly upward, the gravity differentiation of hot and cold water, as well as the fact that thermal conductivity of surrounding rock is worse than that of reservoir, the thermal energy in edge and bottom water mainly transfers upward with less heat loss and most accumulates in the oil reservoir and the edge bottom water layer above the horizontal wells plane; edge and bottom water resources are abundant and environmentally friendly, therefore the method of electric heating edge and bottom water can be recycled.
 9. The method according to claim 1, 7 and 8 wherein the electric heating system positioned in the horizontal well comprising: the electric heaters generate resistance heat, and directly heats the edge-bottom water; the formation water moving up and down generate induced current and induced heat due to the electrical conductivity of water provided that the electric heaters connect with current;
 10. The method according to claim 1 wherein the electric immersion heater preferably includes a thermocouple operatively connected to the surface power unit for monitoring heating time and the temperature of the edge-bottom water; and further to control the pressure of the oil reservoir according to the congruent relationship between boiling point and pressure of water.
 11. The method according to claim 1 comprising the gradually accumulated reservoir pressure and temperature can be released with some production wells to prevent cracking in closed reservoirs; the electric immersion heater preferably includes a thermocouple operatively connected to the surface power unit for monitoring heating time and heating temperature, accordingly, further to control the pressure of the oil reservoir according to the congruent relationship between boiling point and pressure of water. under a certain pressure below the reservoir fracture pressure, continuously electric heating the upper part of edge and bottom water at a higher temperature for a long time. under a certain pressure below the reservoir fracture pressure, continuously electric heating the upper part of edge and bottom water layers by pressure relief through production wells at a higher temperature for a long time.
 12. The method according to claim 1 wherein temperatures in all oil layers rise to the point needed by continuously electric heating the edge and bottom water layers, and wherein the temperature of the oil reservoir for effective oil thermal recovery increases at least to the rang of 80° C. to 150° C.; continuously centralized electric heating the edge and bottom water at a temperature of the edge and bottom water around the immersion heater lower than 450° C.
 13. The method according to claim 1 wherein the greater the depth of the edge and bottom water layer, less electrical energy required to heat the edge and bottom water layer, due to the reasons comprising, the smaller the temperature difference between temperature of formation water and boiling point, less heat energy needed; the greater the temperature difference between the temperature of formation water and surface water, less heat energy required; no heat loss of wellbore and pipeline, the greater the depth of the reservoir, the less energy needed; less electric energy needed in secondary oil recovery due to high reservoir temperature.
 14. The method according to claim 1 comprising centralized excavating the crude oil with at least one or more production wells wherein the production wells can be horizontal wells or vertical wells or a combination of vertical and horizontal wells.
 15. The method according to claim 1 including during centralized recovering the mobilized oil with at least one or more production wells, a variety of thermal recovery mechanisms are used consisting of: the thermal expansion pressure from water formations and oil layers; the effect of synthesis steam flooding produced by water soluble gas overflow, steam coming from edge and bottom water as well as pore water, and pyrolysis gas from crude oil in bottom oil reservoirs; hot water flooding due to edge and bottom hot water coning; the viscosity-reduction effect/wax-precipitation effect of in-place oil under high temperature; gravity drainage of the heated crude oil; gravity differentiation among fluids after primary-centralized thermal recovery of oil for another times, and combinations thereof.
 16. The method according to claim 1 comprising after the completion of primary oil recovery, the residual oil and water in reservoir can be separated by gravity differentiation over time, and the formation water can be re-heated for secondary oil recovery.
 17. An electric heating system comprising, an inner liner divided by a heat insulation board comprising upper half of the inner liner slotted and lower half of the inner liner vacuum-sealed; and the heat insulation board is set at a horizontal diameter of the inner liner, a sealing board is provided on either side of the lower liner; wherein the lower liner, in cooperation with the heat insulation board, insulates heat, and the lower part of the liner is vacuum-sealed by the sealing board and the heat insulation board to reduce downward transmission of thermal energy; waterproof spiral electric heaters in series connection are provided on the heat insulation board in the middle part of the upper part slotted of the liner; several ferrite permanent magnet rods are fixed at the inner top of the upper liner;
 18. The system according to claim 17 wherein the upper half of the inner liner slotted allowing fluids to transfer freely, and supporting the pressure of overlying formations; suspending the ferrite permanent magnet rods.
 19. The system according to claim 17 wherein electric heaters connected in series generate resistance heat, and directly heat edge-bottom water; the electric heaters connected with current generate electromagnetic field, together with ferrite permanent magnetic field, which makes the formation water moving up and down generate induced current and induced heat due to the electrical conductivity of water.
 20. The system according to claim 17 wherein at least one ferrite permanent magnet-rod is arranged to reduce scaling of the electric heater.
 21. The system according to claim 17 wherein the lower half of the inner liner vacuum-sealed to prevent thermal energy from transferring downwards; a heat insulation board set at a horizontal diameter of the inner liner to prevent thermal energy from transferring downwards; a sealing board set at two sides of the lower half of the inner liner in cooperation with the heat insulation board to prevent thermal energy from transferring downwards, and keep the stability of the lower half of the inner liner. 